The present disclosure relates to a PLC system and more particularly, to a PLC system that may sufficiently control the industrial site and efficiently perform a web based service.
In recent, industrial equipment, such as a programmable logic controller (PLC) is increasing the support of a web based service, such as a hypertext transfer protocol (HTTP), file transfer protocol (FTP), simple network time protocol (SNTP), simple mail transfer protocol (SMTP), etc. service.
That is, the PLC checks the state of control equipment at a remote place through web server support using the HTTP and receives data on equipment using the FTP. Also, the PLC uses the SNTP for time synchronization through a network and uses an SMTP service to transmit, what the control equipment experiences, to a user through an e-mail.
FIG. 1 is a protocol architecture diagram for a general web based service, a Transmission Control Protocol layer (TCP) 11 and an Internet Protocol (IP) layer 12 performs a function of transmitting data to a destination, and an application layer 13 is located on the TCP/IP layers 11 and 12 and functions as an interface between a system and a user to provide a service that the user desires.
A service configuring the application layer 13 includes SMTP, FTP, SNTP, data communication, etc. and data transmitted from the TCP/IP layers 11 and 12 to the application layer 13 is analyzed and processed in an application layer service suitable for a data characteristic.
In this case, the data communication service transmits and receives information on industrial equipment or control data, and the web based service controls a system along with the data communication service or provides data processed as desired by a user.
FIG. 2 is a flowchart of the operation of a PLC system conforming to typical scan synchronization batch processing, which is a method in which input data is first processed, data is processed according to a user-defined control program and then a processed result is applied to an output.
In this case, when the PLC system starts an operation, a scan operation is performed in step S21. That is, when input image region refresh is performed in step S21-1, an operation is performed by using a scan program in step S21-3, and the operation is completed, output image region refresh is performed in step S21-5.
After the scan operation in step S21, the PLC system determines whether web based service processing is required in step S23, and when the web based service processing is not required, the scan operation is again performed in step S21, and when the web based service processing is required, a web service is performed in step S25 and then the scan operation is performed in step S21.
Thus, the web based service in the PLC system conforming to the typical scan synchronization batching processing requires an operation separated from the scan operation.
Since system control at the industrial site highly considers quick data processing and response, a scan time works as an importance criterion that determines the quality of equipment.
The web based service, such as an HTTP, FTP, SNTP, SMTP, etc. service does not cause a system a load before a user requests a service, but as soon as an operation is performed, processing a lot of data is required.
Processing a lot of data for the operation of the web based service works as a reason for an increase in scan time. As a result, it affects the control process of industrial equipment, so it is possible to cause the malfunction of a system.
On the contrary, when the data processing of the web based service is restricted in order to minimize an impact that the web based service has on the control process of the industrial equipment; the web based service may not smoothly be performed.